(a) Field of the Invention
The invention relates to the field of tissue engineering, production of connective tissue linked to natural bones or synthetic bone substitutes (tendons, ligaments, cartilage, etc.) can benefit from the invented procedure. The procedure of the present invention is carried out to produce bioengineered connective tissue substitutes. Connective tissue substitutes (CTS) of the invention may be constructed for replacement of ligaments, and most particularly cruciate ligaments or tendons.
(b) Description of Prior Art
Researchers in the surgical arts have been working for many years to develop new techniques and materials for use as grafts to replace or repair damaged or torn tissue structures, particularly bones and connective tissues, such as ligaments and tendons, and to hasten soft tissue repair. It is very common today, for instance, for an orthopedic surgeon to harvest a central portion of patellar tendon of autogenous or allogenous origin for use as a replacement for a torn cruciate ligament. The surgical methods for such approaches are well known. Further it has become common for surgeons to use implantable prostheses formed from plastic, metal and/or ceramic material for reconstruction or replacement of physiological structures. Yet despite their wide use, surgically implanted prostheses present many attendant risks to the patient. It will suffice to say that surgeons are in need of a non-immunogenic, high tensile strength graft material which can be used for surgical repair of bones, tendons, ligaments and other functional tissue structures.
One of the most widely used anterior cruciate ligament (ACL) substitutes is the bone-patellar tendon-bone graft. The central one-third of the patient's or a donor's patella tendon, along with portions of the bony insertions of the patella tendon, is used as a replacement for the damaged ACL. The bony insertions are harvested as bone fragments to facilitate implantation and fixation of the replacement graft into osseous tunnels performed in the tibia and femur in the patient's knee joint. The bone-patellar tendon-bone graft is a popular choice for ACL reconstructive surgery because of its high load strength after six weeks and its functional bone fixation.
Some fixation devices employ various structures for coupling with a ligament or a suture and for engaging with the bone. For example, U.S. Pat. No. 5,356,435 discloses an element for fixing a ligament in a bony tunnel. The element includes an internal conduit for receiving an end of a ligament, and a clamping structure for securing the ligament end within the conduit. U.S. Pat. No. 5,356,413 to Martins et al. discloses a surgical anchor having a body portion and a suture-receiving bone. Another commonly used ACL substitute is the iliotibial band graft. The iliotibial band is a section of ligament which is harvested from a portion of a patients or a donor's iliotibial ligament located within the anterolateral ligament structures of the knee joint. The major problem with these techniques is that another part of the body, or the joint of the donor is often significantly weakened after biopsied to get grafts. Long term drawbacks of this approach are that chronic pain, patellar fractures, knee instability and cartilage degeneration.
Researchers have been attempting to develop satisfactory polymers or plastic materials to serve as ligament or tendon for other connective tissues replacements. It has been found that it is difficult to provide long-term solution using these materials to permanently replace connective tissues.
Artificial materials based on network fibers made of polyester or polytetrafluoroethylene have been used extensively as replacements for ligament and tendon, with some success. However, persistent inflammatory reactions occur following wear off of particles upon time post-implantation. Additionally, they do not readily breakdown and are not readily integrated with the body via remodeling by tissue cells.
Bioengineered tissues can be used as grafts implants or prostheses to replace damaged tissues.
U.S. Pat. No. 5,855,619 of Caplan discloses the use of a filament as load-bearing member of a contracted gel matrix containing mesenchymal cells. The implant described in this patent allows partial repair of connective tissues by attaching the implant to the tissue to be repaired. However, since this implant is constructed without anchoring extremities, the anchorage capability is limited.
Fibroblast-populated Collagen gels (FPCG) constitute an interesting in vitro model of soft tissues to investigate tissue response to various biological, chemical, electrical, and mechanical stimuli. In the past year, the potential of using a ligament-shaped FPCG to produce a bioengineered anterior cruciate ligament (ACL) has been investigated. Mechanical properties of FPCG are known, however, to be significantly lower than those required for a functional ACL. Finding ways to improve their mechanical properties would be highly beneficial not only for improving a ACL but also for the tissue engineering field in general.
It is therefore an object of the present invention to provide an implant and method of preparation thereof which obviates the disadvantages of the prior art approaches.